Yep - you won't be able to "see" the mysql users passwords but you will be able to reset accordingly.
Get the password from one of the conf files and do something like:
SET PASSWORD FOR 'ispconfig'@'localhost' = PASSWORD('password');
Again, you will soon know if you have it right because all the sql errors you're reported before about lookups should go away.
While you're there have a poke around at phpmyadmin 4.0.3 - latest released version with bug/security fixes. May or may not be appropriate for your platform.